The technical field relates to devices having both a capacitive and resistive functions, and methods of incorporating such devices in organic dielectric laminates and printed wiring boards.
Capacitors and resistors may be used in series for transmission line termination of signal traces extending between integrated circuit (IC) devices. The capacitors and resistors are used to match the impedance of an IC device to a line, or to reduce or eliminate signal reflection. Some circuits are continuous load and use a resistor in parallel with the line. Non-continuous load circuits have a resistor and capacitor in series and are useful for low power ICs. FIG. 1 schematically illustrates a non-continuous load termination of IC devices 10 and 20.
In FIG. 1, the distance from a to b is typically short. The value of the resistor R is chosen to match the line impedance and is typically about 45-80 ohms. The value of the capacitor C is chosen so that the RC time constant of the resistor R and the capacitor C in series is greater than the rise time of a signal and less than the total time of the signal pulse. Typical capacitance values are on the order of 30 picoFarads.
Conventional RC terminations are typically constructed of a surface mount technology (SMT) resistor and capacitor. FIG. 2 is a cross section view of a portion of a printed circuit board 25 having a SMT resistor 40 and a SMT capacitor 50 connected to an IC device 30 to form a conventional SMT RC transmission line termination for the IC 30. The signal line carrying the signal to the IC 30 is connected to a circuit trace 60 connecting the IC device 30 to the resistor 40. The capacitor 50 is coupled to a circuit trace 70 by one of a pair of solder pads 52 and solder joints 58. The resistor 40 is coupled to the circuit trace 70 by a solder pad 42 and a solder joint 48. The capacitor 50 is coupled to a via hole 80 by the other solder pad 58 and a circuit trace 59. This arrangement places the resistor 40 and the capacitor 50 in series with the signal line and connected to ground through a plated through-hole via 80. This conventional surface mount approach requires use of valuable surface real estate. Further, the requirement for solder joints reduces reliability and increases costs of fabrication.